Gavin Grimm leans on a post on his front porch during an interview at his home in Gloucester, Va., Aug. 25. Schools can’t prevent transgender students from using the restrooms that correspond with their gender identities without violating federal law, the Obama administration says. The government’s filing says a Gloucester County School Board policy that requires Grimm to use either the girls’ restrooms or a unisex bathroom constitutes unlawful bias under Title IX, the 1972 law that prohibits sex discrimination in education.

The argument was initially put forward by the Department of Education (DOEd) and the Department of Justice (DOJ) in a friend-of-the-court brief backing a Virginia teenager named Gavin Grimm who is suing for the right to use the boys’ restrooms at his Virginia high school.

The brief suggests that the Gloucester County School Board's requirement that Gavin must use either the girls’ restrooms or a unisex bathroom can be considered unlawful bias under Title IX, the federal law prohibiting gender-based discrimination.

The policy prevents Gavin from enjoying “a benefit that every other student at this school enjoys: access to restrooms that are consistent with his or her gender identity," lawyers with DOEd and DOJ wrote in their filing. “Treating a student differently from other students because his birth-assigned sex diverges from his gender identity constitutes differential treatment on the basis of sex under Title IX."

The brief, while not legally binding, "sends a crucial message to schools across the country – transgender youth are valuable members of our community who are entitled to full protection of the law," Human Rights Campaign President Chad Griffin told the Associated Press. "No one should be humiliated or marginalized by the adults responsible for helping them to achieve."

Gavin was born female but identifies as male. He came out as transgender to his parents in the spring of 2014, and was allowed to use the boys’ restrooms at Gloucester High School until some other families complained. The school board then voted to restrict transgender students to single-stall unisex facilities and those bathrooms that correlate with their biological sex.

The American Civil Liberties Union sued to overturn that policy in June, claiming that the policy was grounds for sex discrimination.

In July, when the Justice Department first expressed a desire to weigh in on Gavin’s lawsuit, Gloucester County Attorney Ted Wilmot told the Daily Press newspaper in Newport News, Virginia that “existing court precedents do not support the idea that the school board's restroom rules violate Title IX.”

In September, a federal judge sided with the school board, dismissing the ACLU’s sex discrimination claim. The case is now pending before the 4th US Circuit Court of Appeals.